Reduction of shrinkage and brittleness for resorcinol-formaldehyde aerogels by means of a pH-controlled sol–gel process

• Synthesis of novel resorcinol-formaldehyde aerogels using a pH-controlled sol–gel process.
• Analysis of density, microstructure, BET surface, thermal and mechanical properties.
• Gels are less brittle than Pekala-type aerogels.
• Shrinkage is significantly reduced when compared to conventional aerogels.

Aerogels have attracted remarkable attention as porous low-density superinsulating material. However, they are typically brittle and tend to shrink during preparation or work-up preventing their use as a composite material. In that context, we have developed a sol–gel-process towards resorcinol-formaldehyde aerogels that includes a precise pH-adjustment at an early stage of the polymerization. As a result, less brittle analogues of Pekala aerogels were obtained that resemble Pekala gels in many aspects (skeletal density, porosity, thermal properties). However, significant differences were found in terms of inner surface area and compressive modulus, which are smaller for lower pH-values. Since pH-adjustment leads to minimal gel shrinkage, this sol–gel-process may be useful for the development of aerogel composites.

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